1. Technical Field
The invention relates to a process for producing toner for electrophotographic use and an image forming method employing the toner.
2. Related Art
Recently, the main stream of the image forming by electrophotographic system is shifted to the digital system. In the image formation by the digital system, a toner having small diameter is used so as to realizing superior fine line reproducibility and high resolution such as development of a small dot image on the level of 1,200 dpi; dpi is the number of the dot per 2.54 cm. Japanese Patent Publication Open to Public Inspection, hereinafter referred to as Japanese Patent O.P.I. Publication, No. 2002-296839, Paragraph 0011, and No. 2002-351140, Paragraph 0011, describe a toner producing method as an example of production of such the small diameter toner, in which raw materials of the toner such as polyester resin are dispersed in an aqueous medium and the resin particles in the emulsion are coagulated so as to form particles having the size of the toner.
As an embodiment of the digital image formation, a print on demand system for “necessary copies at necessary time” is performed. The image formation by such the system is noted as a system to be applied in place of light printing since the plate making to be performed in the usual printing process is not necessary and the publishing of several hundreds copies of books is possible, and direct mails or invitation cards each having different address can also be printed.
It has been found that the electrophotographic image formation causes a problem on the preparation of a mail or an invitation card each having a different address. The problem is that a sufficient fixing effect is difficultly obtained when the image is formed on a thick paper such as an invitation card to a marriage party, a mourning mail card or a card regarding funeral rites. Particularly, in the mourning mail card or the card regarding funeral rites having a gray colored frame, the gray frame is difficultly fixed and the unfixed toner causes the contamination of the hand of the handler or the paper surface.
Moreover, when the toner image is formed on the thick paper, considerably larger stress is applied to the toner comparison to that when the toner image is formed on usual paper such as copy paper. Consequently, the toner is easily destroyed on the occasion of the image formation and a problem is raised that the paper surface is contaminated by fine particles formed by the crush of the toner particle.
The mourning mail card is one of the recording media having the highest difficulty, and other than that it is necessary for diffusing the electrophotographic system as the on demand image forming system that the toner image can be stably formed not only on paper developed for electrophotographic use but on the paper for printing. The electrophotographic system is difficultly accepted by the field of printing industry as long as such the condition is not cleared.
Moreover, it is often seen that a commuter reads a paperback held in one hand while holding him on to a strap by another hand. The copy is required-a sliding ability capable of turning over the page of the book by one hand in such the situation and a strength of the sufficient fixation strength of the toner so that the toner does not contaminate the paper surface or the characters by friction.
The toner image by the electrophotography, however, is not accepted by the publisher since the sliding ability and the fixation strength of the image is inferior to those of the usual printed material. Therefore, the diffusion of the electrophotography in this field has been delayed.
Furthermore, when a lot of prints are copied by a copying machine utilizing a trickle method, by which large stress tends to be loaded to the toner particles, a trouble is raised that the interior of the equipment is contaminated since the toner particles are crushed or the external additive is buried into the toner particles so as to the charged amount of the toner cannot be held at a constant level and the particles unstably charged are scattered.
Consequently, atoner production method, a toner and an image forming method are required, which are superior in the fixing ability on the thick paper or paper for offset printing, toner blister is not formed and the contamination in the machine caused by the toner scattering does not occur when a lot of prints are copied.